1. Field of the Invention
The present invention relates to a method for doping a material layer with antimony, by ion implantation.
2. Description of the Related Art
The reduction in critical dimensions necessary for continued gains in dynamic random access memory (DRAM) circuit density will require a number of fundamental changes from current practice, relative to the techniques and source materials employed in current manufacturing practice. As geometries of such DRAM devices decrease below 0.35 micrometer, a corresponding reduction is necessary in the size of p/n dopant layer thicknesses and in the associated dopant concentrations.
These factors, coupled with the need to precisely tailor ion implant distribution profiles, will greatly complicate the practice of ion implant technology in the manufacture of future generation memory devices. The mobility of lightweight boron (p-type) and phosphorous (n-type) dopants is too high, even with reduced thermal budgets, to accommodate the increased stringency of future implant requirements. Indium (p-type) and antimony (n-type), with their significantly greater size and mass, will need to be used to improve control of ion throughput and device threshold voltage, and to reduce channeling effects in the fabricated structures.
Beam current is roughly proportional to the extraction energy. Accordingly, use of lower energy acceleration for shallower implants of current dopants results in greatly decreased beam intensities. The trend to lower energies to shape reduced geometry implants has prompted an investigation of the use of larger fragments e.g., BF.sub.2 rather than B per se. Fluorine, however, enhances diffusion of boron in SiO.sub.2 which results in contamination of the well region and loss of threshold voltage control in the resulting devices. Greater control of ion implant profiles, using heavier ions such as indium and antimony in future DRAM manufacturing, will markedly reduce the need for angled implants which are currently required to prevent channeling and to effect required implant geometry.
Accordingly, the art is in need of new source compositions for elements such as indium and antimony, for ion implant applications.
U.S. Pat. No. 4,496,843 issued Jan. 29, 1985 to K. Kirita, et al., describes a method of producing metal ions of various metals. Antimony ion generation is described, utilizing trialkyl antimony compounds and trialkoxy antimony compounds. This patent also discloses the use of a fluoride gas as an auxiliary gas for preventing organic metal compound decomposition products from attaching to the inner wall of the arc discharge chamber during processing.
U.S. Pat. No. 4,988,640 issued Jan. 29, 1991 to D. A. Bohling, et al., describes the use of at least partially fluorinated organometallic compounds in reactive deposition (ion implant) applications, utilizing source compounds of the formula MR.sub.1 R.sub.2 R.sub.3 wherein M is arsenic, phosphorous or antimony, and R.sub.1, R.sub.2 and R.sub.3 are each, separately, hydrogen or an organic radical, wherein at least one R is an organic radical which is at least partially fluorinated. The organic radicals may be alkyl, cycloalkyl, aryl, alkenyl or arenyl.
U.S. Pat. No. 5,124,278 issued Jun. 23, 1992 to D. A. Bohling, et al., describes the use of amino-substituted metallic donor source compounds for reactive deposition (ion implant) applications. The disclosed source compounds have the formula M(NR.sub.2).sub.3-x H.sub.x, where R is an organic radical selected from the group consisting of alkyl, cycloalkyl, aryl, alkenyl, arenyl or fluoroalkyl, x is less than or equal to 2, and M is arsenic, antimony or phosphorous.
It is an object of the present invention to provide an improved source composition for ion implantation of antimony ions.
It is another object of the present invention to provide a source composition for n-doping a material layer with antimony by ion implantation, in which the source composition avoids deposition of certain ionization reaction by-products on interior (wall) surfaces of the ionization chamber of the ion implant system.
Other objects and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.